WASHINGTON, Oct 20 (Reuters) - U.S. regulators are examining the growing number of nutrition claims found on the front of food packages after complaints that they give a misleading picture of their health benefits, officials said in a warning to food companies on Tuesday.

The Food and Drug Administration is trying to determine if any claims violate federal food labeling rules and “will take enforcement action against any egregious examples,” FDA Commissioner Margaret Hamburg told reporters.

FDA officials also are developing a proposed regulation to define nutritional criteria for claims made on the front of food packages, Hamburg said.

The FDA is acting as companies increasingly add nutrition claims to the front of packages to catch the attention of hurried shoppers who might not read the detailed facts about a food’s content on the back, she added.

“Some nutritionists have questioned whether this information is more marketing-oriented than health-oriented, and judging from some of the labels that we have seen, we think this is a valid concern,” Hamburg said.

In a letter to food companies, the agency said it was “currently analyzing (front-of-package) labels that appear to be misleading.”

Asked to give examples of questionable claims, Hamburg said some foods with almost 50 percent sugar were displaying a “Smart Choices” checkmark. Other package fronts boast a high percentage of the recommended daily vegetable intake but fail to mention that the products contain 80 percent of the suggested fat allowance, she said. She did not name specific products.

With a wide variety of symbols and claims being used, the FDA is exploring if consumers would benefit from a single symbol for the front of packages to give a quick and accurate idea of nutritional content, Hamburg said.

Mike Hughes, chairman of the Smart Choices Program, said it “complies with all U.S. laws and regulations” and “we believe in the science behind” the program.

“We look forward to the opportunity to participate in FDA’s initiatives,” Hughes said in a statement.

The Grocery Manufacturers of America (GMA), a trade group representing food makers, said it would work with the FDA to determine what information was most useful to consumers.

“Manufacturers have already introduced or reformulated over 10,000 products to reduce calories, sugar, sodium, fat and trans fat or to enhance their nutritional profile, such as with the addition of whole grains or minerals,” GMA President Pamela Bailey said in a statement.

U.S. Rep. Rosa DeLauro, a Democrat, said she was “very encouraged by FDA’s commitment to proceed with enforcement actions” against unauthorized claims.

“Clearly something is wrong when foods such as Froot Loops cereal, Cookie Crisp cereal, and Uncle Ben’s Instant Rice are designated as ‘healthy’ by these labeling systems,” DeLauro said.

A Kellogg spokeswoman referred to the statement from the Smart Choices Program. Officials at General Mills and Mars did not immediately respond to requests for comment. (Reporting by Lisa Richwine, editing by Matthew Lewis)